A proposal for plastic hinges modification factors for damaged RC columns

This paper proposes experimental based formulations for modifying the moment-rotation plastic hinges of RC columns that have entered the plastic range, introducing suitable expressions of modification factors for stiffness, strength and displacement capacity as a function of the rotational ductility demand. Those expressions may be used in order to assess the performance loss of a building that has been damaged by an earthquake. Considering typical RC members of buildings in Mediterranean regions, with design characteristics non-conforming to present-day seismic provisions, a database of 23 cyclic tests results on columns reinforced with deformed bars and of 13 tests for columns with smooth bars was assembled and studied. The trends resulting from experimental data show that member's stiffness decreases quite steeply with ductility demand, while an almost parabolic increase with ductility of the ratio of residual drifts versus yielding drift ratio can be observed. The obtained modification factors can be used to simulate the damage state in RC members that have experienced a given ductility demand after an earthquake, either retrieved via analytical simulations (e.g. pushover analyses) either inferred by observation of real damage on the structural elements.